1. Field of the Invention
The present invention relates to a control system and method for an internal combustion engine which includes a variable valve-operating mechanism which is capable of continuously changing the lift of an intake valve, and an intake air amount-adjusting valve which is disposed at a location upstream of the intake valve and is capable of adjusting the amount of intake air.
2. Description of the Related Art
As a control system for an internal combustion engine of this kind, there has been proposed a method disclosed in Japanese Laid-Open Patent Publication (Kokai) No. 2003-172189. In this control system, to stabilize the amount of intake air during a time period over which the conditions of automatic operation of the engine are not stable, control of the intake air amount by a variable valve-operating mechanism is inhibited, but performed by control of an intake air amount-adjusting valve. Further, at this time, the time period over which the intake air amount control by the variable valve-operating mechanism is to be inhibited is set according to the number of automatic stops or number of automatic starts of the engine, and if the number is small, the time period is set to be short.
In the conventional control system for an internal combustion engine, for some time after the start of the engine, the number of times of automatic stops or number of times of automatic starts of the engine is small, and hence the time period over which the intake air amount control by the variable valve-operating mechanism is to be stopped is set to be short. Therefore, there is a fear that the variable valve-operating mechanism starts to be operated before lubrication oil for lubricating the variable valve-operating mechanism is sufficiently distributed throughout the mechanism, causing the problems of abrasion, damage, etc. due to insufficiency of the lubrication oil.